Summary Objective To identify factors associated with smoking and heavy alcohol consumption among women of reproductive age. Study design Cross-sectional study. Methods Data from 5031 women aged 20–49 years who participated in the Fourth Korean National Health and Nutrition Examination Survey 2007–2009 were analysed. Variables were classified as sociodemographic factors, psychological factors, gynaecological factors and chronic conditions. Factors that influence high-risk behaviours associated with adverse pregnancy outcomes were identified using multiple logistic regression analysis. Results Among women of reproductive age, prevalence rates of smoking, heavy alcohol consumption and both were 7.3%, 21.4% and 4.3%, respectively. Among the sociodemographic factors, young age, a lower level of education and unmarried status were more likely to be associated with high-risk behaviours such as smoking, heavy alcohol consumption and both. Psychological factors such as stress intensity and suicidal ideation were also significantly associated with all the above-mentioned high-risk behaviours. In addition, an association was found between high-risk behaviours and oral contraceptive use. Conclusions Identifying the factors associated with high-risk behaviours may help in the design of interventions to decrease the prevalence of smoking and heavy alcohol consumption. Population-level reduction of these high-risk behaviours among women of reproductive age may improve pregnancy outcomes and also decrease the prevalence of chronic diseases, including cancer, in the long term.